The aim of this project is to elucidate the neuronal (CNS) mechanisms that mediate the effects in vivo of several hallucinogens and other pharmacologically or functionally related compounds. To this end, a sensitive and specific "behavioral assay," in which rats (or other animals) are trained to detect (discriminate) drug-induced alterations in their own internal environment (states), will be used to systematically investigate several agents which either directly or indirectly alter the functional activity of serotonin (5-HT) or dopamine (DA) containing neurons (or both). These include: (1) congeners of LSD such as psilocybin which, like LSD, is a potent hallucinogen or psychotomimetic in humans and lisuride which has been reported to have many, if not all, of the pharmacological and electrophysiological properties of LSD but is not hallucinogenic; (2) fenfluramine (FF), a compound that resembles amphetamine structurally as well as clinically (both drugs are used to treat obesity by suppressing appetite) but which acts primarily by releasing 5-HT rather than DA from pre-synaptic terminals; (3) phencyclidine (PCP), a dissociative anesthetic and dangerous drug of abuse, the effects of which have been described as schizophrenomimetic.